Why do I get "Warning: os-prober will not be executed to detect other bootable partitions." after running "apt upgrade"?

Question

I'm running Ubuntu 22.04 and everything was fine. Today I did sudo apt update && sudo apt upgrade and at the end I got the following warning:

Sourcing file `/etc/default/grub'
Sourcing file `/etc/default/grub.d/init-select.cfg'
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-5.15.0-39-generic
Found initrd image: /boot/initrd.img-5.15.0-39-generic
Found linux image: /boot/vmlinuz-5.15.0-37-generic
Found initrd image: /boot/initrd.img-5.15.0-37-generic
Memtest86+ needs a 16-bit boot, that is not available on EFI, exiting
Warning: os-prober will not be executed to detect other bootable partitions.
Systems on them will not be added to the GRUB boot configuration.
Check GRUB_DISABLE_OS_PROBER documentation entry.
Adding boot menu entry for UEFI Firmware Settings ...
done

From what I have seen, os-prober is used when multiple OS are installed on the same machine, so why is this warning on? I have only Ubuntu 22.04 installed. Is it because of the two kernels found?

Memtest86+ already solved in the comments, but what about os-prober?

Here is the content of /etc/default/grub:

# If you change this file, run 'update-grub' afterwards to update
# /boot/grub/grub.cfg.
# For full documentation of the options in this file, see:
#   info -f grub -n 'Simple configuration'

GRUB_DEFAULT=0
GRUB_TIMEOUT_STYLE=hidden
GRUB_TIMEOUT=0
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
GRUB_CMDLINE_LINUX=""

# Uncomment to enable BadRAM filtering, modify to suit your needs
# This works with Linux (no patch required) and with any kernel that obtains
# the memory map information from GRUB (GNU Mach, kernel of FreeBSD ...)
#GRUB_BADRAM="0x01234567,0xfefefefe,0x89abcdef,0xefefefef"

# Uncomment to disable graphical terminal (grub-pc only)
#GRUB_TERMINAL=console

# The resolution used on graphical terminal
# note that you can use only modes which your graphic card supports via VBE
# you can see them in real GRUB with the command `vbeinfo'
#GRUB_GFXMODE=640x480

# Uncomment if you don't want GRUB to pass "root=UUID=xxx" parameter to Linux
#GRUB_DISABLE_LINUX_UUID=true

# Uncomment to disable generation of recovery mode menu entries
#GRUB_DISABLE_RECOVERY="true"

# Uncomment to get a beep at grub start
#GRUB_INIT_TUNE="480 440 1"

Answer 1

The warning is generated by /etc/grub.d/30_os-prober, take a look at the lines 43 to 59:

if [ "x${GRUB_DISABLE_OS_PROBER}" = "xtrue" ]; then
  grub_warn "$(gettext_printf "os-prober will not be executed to detect other bootable partitions.\nSystems on them will not be added to the GRUB boot configuration.\nCheck GRUB_DISABLE_OS_PROBER documentation entry.")"
  exit 0
elif [ "x${GRUB_DISABLE_OS_PROBER}" = "xauto" ]; then
  # UBUNTU: We do not want to disable os-prober on upgrades if we found items before.
  if test -e /boot/grub/grub.cfg && ! grep -q osprober /boot/grub/grub.cfg; then
    grub_warn "$(gettext_printf "os-prober will not be executed to detect other bootable partitions.\nSystems on them will not be added to the GRUB boot configuration.\nCheck GRUB_DISABLE_OS_PROBER documentation entry.")"
    exit 0
  fi
fi

if ! command -v os-prober > /dev/null || ! command -v linux-boot-prober > /dev/null ; then
  # missing os-prober and/or linux-boot-prober
  exit 0
fi

grub_warn "$(gettext_printf "os-prober will be executed to detect other bootable partitions.\nIts output will be used to detect bootable binaries on them and create new boot entries.")"

You have several options:

• Ignore the warning, it's only a warning, not an error.

• Set the variable GRUB_DISABLE_OS_PROBER=false in /etc/default/grub. The warning will change to os-prober will be executed to detect..., as we can see in the snippet of the script.

• Remove the executable bit from /etc/grub.d/30_os-prober. This will prevent the execution of the script, so you can't get any of this warnings. You can do that with:

  sudo chmod -x /etc/grub.d/30_os-prober
  

• Edit the script /etc/grub.d/30_os-prober. If you comment out the lines with grub_warn, the script will run without issuing these warnings.